JPH06281112A - Method for utilizing discharge gas/in circulating fluidized bed type boiler - Google Patents

Abstract

PURPOSE:To enable supplying of gas to a seal device in a coal supplying system to be independent from a system of flowing air and combustion air and further to enable interference in control of their relative states to be eliminated. CONSTITUTION:A circulation fluidized bed type boiler is provided with a discharged gas circulation system which is independent from a flowing air control and combustion air control system. Discharged gas is supplied from the system as sealing gas A between a solid fuel feeding port 16 and a surrounding part, cushion gas B for dampening shock of the solid fuel against a supplying pipe 17 for a combustion chamber and the like, dispersion gas C aiming at feeding the solid fuel uniformly with a section part of the combustion chamber and particle flowing circulation gas D for a pneumatic valve 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention aims to utilize a circulating fluidized bed boiler, which uses solid matter such as coal as a fuel, and in particular, its exhaust gas, to easily secure a required superficial velocity by primary air in a low load region. It is related to the structure.

[0002]

2. Description of the Related Art FIG. 2 shows the structure of a conventional circulating fluidized bed boiler. Coal and limestone (desulfurizing agent) are supplied onto the lower air dispersion plate 2 in the boiler body 1, and an auxiliary bed material made of silica sand, ash, etc. is supplied from an auxiliary circulation particle bin (not shown).

Combustion air is supplied from the primary air forced draft fan 3 through the air preheater 12 and the primary air supply pipe 5 to the lower side of the air dispersion plate 2 and the secondary air forced draft air. It is divided into secondary air for two-stage combustion, which is supplied from the side wall of the combustion chamber 7 from the machine 4 through the air preheater 12 and the secondary air supply pipe 6, and the primary air and the secondary air have an approximately theoretical air ratio. In the above, the fuel is burned on the dispersion plate 2 while fluidizing the medium particles composed of the input solid fuel and the circulating solid fuel, the combustion ash, the desulfurizing agent, the auxiliary bed material and the like.

The fuel and medium particles are discharged from the combustion chamber 7 together with the combustion exhaust gas along with combustion, pulverization, desulfurization reaction, etc. in the combustion chamber 7, and coarse particles are hot cyclone 8 which is a particle collector.
Will be collected at. Coarse particles such as medium particles and combustion ash collected by the hot cyclone 8 can be removed by the pneumatic valve 9
Through the bottom of the combustion chamber 7 to the fluidized bed to enhance the mixing of the circulating particles.

Further, the fine particles that cannot be collected by the hot cyclone 8 together with the combustion exhaust gas, the superheater 10 and the economizer 1.
After passing through 1 and the air preheater 12 and finally completely collected by the dust collector 13, it is discharged from the chimney 15 to the outside of the system by the induced draft fan 14. And pneumatic valve 9
The coarse particles from (1) are recirculated to the bed in the combustion chamber 7 by the air supplied from the bottom and the sides of the pneumatic valve 9.

In the circulating fluidized bed boiler having such a structure, when supplying the solid fuel, the solid fuel is supplied into the combustion chamber by a screw feeder or gravity drop in a "10 mm under" equal mass state. This is a boiler that needs to maintain the lower pressure of the combustion chamber at a positive pressure of several hundreds mmAq due to the pressure loss of the combustion chamber due to the circulating fluidized bed. Therefore, the sealing gas A for sealing at the solid fuel inlet 16 and the cushion gas B for the purpose of reducing collision of the solid fuel with the supply pipe 17 to the combustion chamber and the solid fuel are burned. Combustion chamber 7 for the purpose of evenly charging the chamber cross section
A dispersion gas C provided from the side, a particle flow circulation gas D supplied to the pneumatic valve 9 for returning the particles collected by the cyclone 8 to the combustion chamber 7, and the like are required.

Conventionally, in a circulating fluidized bed boiler which requires these gases, as shown in FIG. 2, the outlet air of the secondary air forced draft fan 4 is branched from the middle of the secondary air supply pipe 6. The air as the sealing gas A, the air as the cushioning gas B, the air as the dispersing gas C, and the air as the particle gas D are obtained by distributing and supplying through the branched path.

[0008]

By the way, in the case of a circulating fluidized bed boiler in which the combustion air is also used for controlling the circulation fluidity, a part of the combustion air is used as the gases A to D as described above. Will sacrifice the control width accordingly. With respect to this point, aiming at securing the minimum superficial velocity for maintaining the flow at the time of low load of the boiler in which the combustion air becomes small, as indicated by the dotted line, on the inlet side of the primary air forced draft fan 3, namely, It has been proposed to mix combustion exhaust gas with combustion air (Japanese Patent Laid-Open No. 63-29103).
No. 04-283304).

However, all of them require a system for controlling the combustion exhaust gas circulation amount according to the boiler load, and the system becomes complicated accordingly. An object of the present invention is to provide a method of utilizing exhaust gas in a circulating fluidized bed boiler, in which a supply system for a sealing gas or the like is made independent from a fluidized air control / combustion air control system, and the above-mentioned complexity is eliminated.

[0010]

In order to achieve the above object, the present invention recycles coarse particles constituting the bed at the bottom of the combustion chamber from the bottom of the combustion chamber to the bed via a cyclone and a pneumatic valve. In the circulating fluidized bed boiler, which discharges the particulates that could not be dispersed by the particle collector together with the combustion exhaust gas through the exhaust gas duct, an exhaust gas circulation system independent from the fluidized air control / combustion air control system is provided. Depending on the system, the sealing gas with the outside at the solid fuel injection port, the cushion gas for the purpose of reducing collision of the solid fuel with the supply pipe to the combustion chamber, etc. The exhaust gas is supplied as a dispersion gas for the purpose of being charged into the fuel cell and as a gas for circulating particle flow to the pneumatic valve.

[0011]

In the prior art, the exhaust gas is mixed into the inlet side of the primary air forced draft fan to maintain the superficial velocity of the primary air supplied from the bottom of the combustion chamber. The sealing air, the cushioning air, the dispersing air, and the particle circulation air, which have been partially supplied to the secondary air supply system, are separated from the secondary air supply system to form an independent system, which is replaced with exhaust gas. This makes it possible to centrally supply the air to be input to the boiler to the primary air and the secondary air,
The control width of these airs can be expanded accordingly.

Further, according to the present invention, since the flue gas is always used only in the relevant place, the exhaust gas circulation system is independent from the system of the fluidized air system and the combustion air system as a system, so that mutual control interference occurs. Eliminates the complexity of the system and removes the traditional complexity.

In pulverized coal-fired boilers of different types, coal, which is a solid fuel, is pulverized and blown into the combustion chamber in the entrained state by the combustion air.
Since the inside of the combustion chamber is maintained at a negative pressure, the above-mentioned gas required in the circulating fluidized bed boiler is not required.

[0014]

The present invention will be described below with reference to the illustrated embodiments. The circulating fluidized bed boiler shown in FIG. 1 has the same basic configuration as that of FIG. 2, and a gas A for sealing the solid fuel input port 16 from the outside and a solid fuel supply pipe 1 to the combustion chamber.
Cushion gas B for the purpose of alleviating the collision with 7, etc., dispersion gas C given to the combustion chamber 7 from the side for the purpose of uniformly injecting solid fuel into the combustion chamber cross section, and cyclone 8. The particles collected in the combustion chamber 7
In order to return to the above, the particle flow circulation gas D or the like given to the pneumatic valve 9 is required.

However, there are differences in the following points. That is,
Exhaust gas circulation system 1 for the sealing gas A, cushion gas B, dispersion gas C, and particle flow circulation gas D
8, the exhaust gas circulation system 18 is a system system independent of the fluidized air control / combustion air control system.

The exhaust gas circulation system 18 takes out a part of the exhaust gas from a portion of the exhaust gas duct after passing through the dust collector (bag filter) 13, that is, from the front side of the ventilator 14, and pipes it to the vicinity of the combustion chamber 7. Exhaust gas circulation pipe 19
From the exhaust gas circulation blower 20 for pressurization provided in the middle of the exhaust gas circulation pipe 19 and the exhaust gas circulation pipe 19 downstream from the blower 20, the sealing gas A, the cushion gas B,
It is composed of branch lines 21, 22, and 23 that branch to the supply parts of the dispersion gas C and the particle flow circulation gas D. There is no flow control damper or the like in the exhaust gas circulation pipe 19 for adjusting the circulation amount according to the primary air / secondary air control.

With this structure, the flue gas is
It is constantly supplied to the solid fuel inlet 16, the portion of the supply pipe 17, the portion of the combustion chamber side portion for dispersion, and the portion of the pneumatic valve 9 for sealing gas A, cushion gas B,
It is used as a dispersion gas C and a particle flow circulation gas D.

As a result, the air introduced into the boiler can be centrally supplied to the primary air and the secondary air.
The control width of these airs can be expanded. Further, the system is independent from the system of the fluidized air control / combustion air control system, and there is no mutual control interference, which has the advantage of simplifying the entire system.

[0019]

As described above, according to the present invention, the following excellent effects can be obtained. Since the exhaust gas circulation system is independent of the combustion air system, there is no mutual control interference and the system is simplified. Further, the air to be introduced into the boiler can be centrally supplied to the primary air and the secondary air, and the control width of these airs can be expanded accordingly.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a circulating fluidized bed boiler showing an embodiment of the present invention.

FIG. 2 is a configuration diagram of a conventional circulating fluidized bed boiler.

[Explanation of symbols]

 1 Boiler Main Body 2 Air Dispersion Plate 3 Primary Air Pushing Fan 4 Secondary Air Pushing Fan 5 Primary Air Supply Pipe 6 Secondary Air Supply Pipe 7 Combustion Chamber 8 Hot Cyclone 9 Pneumatic Valve 10 Superheater 11 Cobber 12 Air Preheater 13 Dust collector 14 Induction drafter 15 Chimney 16 Solid fuel inlet 17 Solid fuel feed pipe to combustion chamber 18 Exhaust gas circulation system 19 Exhaust gas circulation blower 21, 22 and 23 Branch A Seal gas B Cushion Gas C Dispersion Gas D Particle Circulation Gas

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masakazu Furuta 46-59 Nakahara, Tobata-ku, Kitakyushu, Fukuoka 46-59 Nippon Steel Corporation Machinery & Plant Division (72) Fumiaki Hiura Tobata, Kitakyushu, Fukuoka 46-59, Nakahara, Shinjuku-ku, Nippon Steel Corporation Machinery & Plant Division

Claims (1)

[Claims] 1. A combustion exhaust gas in which coarse particles forming a bed at the bottom of the combustion chamber are recirculated from the bottom of the combustion chamber to the bed via a cyclone and a pneumatic valve and entrained with fine particles that cannot be collected by the cyclone. In a circulating fluidized bed boiler that discharges
An exhaust gas circulation system independent of the fluidized air control / combustion air control system is provided, and the exhaust gas circulation system prevents the gas for sealing the outside at the solid fuel injection port and the solid fuel from colliding with the supply pipe to the combustion chamber. To supply exhaust gas as a cushioning gas for the purpose of alleviating the above, a dispersion gas for uniformly injecting solid fuel into the cross section of the combustion chamber, and a gas for circulation of particle flow to a pneumatic valve. Utilization method of exhaust gas in circulating fluidized bed boiler.